1. Field of the Invention
The present invention relates to a camera having an anti-vibration function which corrects for the vibration of a camera such that image vibration does not occur, and, more particularly, to a camera which compensates for anomalies which arise when the anti-vibration function is being performed.
2. Description of the Related Art
Cameras are known which provide an anti-vibration function to counteract image vibration due to hand tremors and the like which occur during hand-held photography. Specifically, the known types of cameras having an anti-vibration function include a vibration correction device which prevents image vibration from occurring due to vibration of the camera, and particularly, due to vibration of the camera caused by tilting or shaking motions. The vibration correction device detects a force received when a body rotates ("coriolis force") by using acceleration sensors and like vibration detection sensors, such as angular velocity sensors or piezoelectric elements. Based upon the result of the detection by the sensors, a main optical system of the camera comprising a photographic lens system, or a portion of the optical system, such as an optical system for vibration correction, is shifted to compensate for vibration in a plane which is orthogonal relative to the optical axis of the main optical system.
In operation, a camera having the above-described anti-vibration function corrects for vibration caused, e.g., by a hand tremor, by detecting the angular velocity of the camera or the acceleration of the vibration of the camera when the hand tremor occurs. An appropriate correction quantity for correcting the image vibration in an imaging plane due to the hand tremor is calculated by a microcomputer or like calculating device based upon the detected angular velocity or acceleration. A lens system for vibration correction which is disposed in a lens barrel of the camera is moved in an up/down, left/right direction, via a drive mechanism, in accordance with the calculated correction quantity to perform a correction of the photographic optical path such that the image in the imaging plane becomes stationary. The above-described vibration correction device utilizes a solenoid, an electromotive motor, or the like as an actuator in order to drive a lens system or prism for vibration correction.
The known cameras having an anti-vibration function suffer from various drawbacks. For example, when an anomaly arises in a vibration detection sensor which detects states of vibrational motion due, e.g., to a hand tremor, and the anomaly in the sensor causes the sensor to produce no output when detecting a hand tremor, the following problem arises. Specifically, when an anomaly in the sensor occurs, correction of the photographic light path is not performed by means of the optical system for vibration correction, a lens system or prism, etc. for vibration correction. As a result, even when correcting for camera vibration caused by a hand tremor using the anti-vibration function, a blurred photograph is taken.
Additionally, even when the sensor acts normally, anomalies arise in a vibration correction optical system which drives a lens system, prism or the like. When correction of the photographic light path is not performed, even when photography is performed with the correction of hand tremor using the anti-vibration function, a blurred photograph is taken. Furthermore, when a blurred photograph was taken, the blurred photograph is not noticed until the film is developed.
Another problem arising in the known cameras having an anti-vibration function, is that when a mechanical type of drive mechanism is used to drive a vibration correction lens system located in a lens barrel of the camera, it is unavoidable that some degree of chatter arises in the gears and the like which comprise the drive mechanism. When the vibration correction lens system is driven in one direction, the chatter is biased to one side. When the drive direction of the vibration correction lens system is reversed, during the interval during which the drive direction is reversed, chatter arises in a reverse direction due to the biased direction of the chatter, and the amount of the chatter becomes a correction error.
Accordingly, because of the existence of the above-described correction error caused by chatter in the mechanical type drive mechanism, image vibration due to chatter remains in the image plane even when photography is performed with a camera having an anti-vibration function.
Yet another problem which arises in the known cameras having an anti-vibration function, is that a phase delay occurs in the output of a vibration detection circuit which includes a vibration detection sensor relative to the input of the vibration detection sensor. The phase delay results from passing the output of the vibration detection sensor through an amplifier to amplify the output from the vibration detection sensor, and then through a filter in order to perform cut-off of noise in the output of the sensor.
Due to the phase delay, a vibration caused, e.g., by a hand tremor, is corrected by the vibration correction lens system with a delay relative to the actual vibration in the image plane. Therefore, even when a vibration correction is performed, the image vibration in the image plane is not completely corrected, and a residual image vibration remains in the image plane.
Further, because of the phase delay caused by passing the output of the vibration detection sensor through an amplifier and filter and the resulting residual image vibration in the image plane, the amount of image vibration in the photographed picture due to residual phase delay is not constant, and varies according to the timing of depression of the release button. Therefore, pictures with large vibration or pictures with small vibration result from photography. The inventors have discovered the above-noted problems and have developed solutions to these problems.